Which material is considered to have a brittle nature but is lightweight and rigid?

The material that is considered to have a brittle nature but is lightweight and rigid is high-tech ceramic. High-tech ceramics are known for their excellent hardness and compressive strength, combined with low density. This makes them ideal for applications where both light weight and rigidity are crucial, such as in watchmaking and other precision instruments.

While carbon is often associated with being strong and lightweight, it can also exhibit variations in brittleness depending on its form (such as graphite versus diamond). Silicon is primarily known for its semiconducting properties and is not typically characterized as rigid in the same sense. Aluminum, although lightweight and used widely in structural applications, is not considered brittle; it is malleable and ductile.

High-tech ceramics, on the other hand, are specifically engineered to be strong yet lightweight while exhibiting brittleness, making them the correct choice in this context.